In recent years, there has been a modulation system using a multi-carrier, which is represented by OFDM system such as WiMAX (for example, IEEE802.16-2004 and IEEE802.16e-2005) as a high speed wireless communication standard that covers communication distance of several kilometers, and long term evolution (LTE) as a standard for next generation mobile telephones. When the modulation system is used, waveforms become like waveforms of signals and noise, and a peak to ratio (PAR), which is a ratio of peak power and average power, becomes large.
In a modulation system such as QAM modulation, which changes both amplitudes and phases, the volume of information that can be transferred is increased due to multiple valuzation. However, because a margin with respect to noise is decreased, it needs to set a preferred carrier to noise ratio (CNR) larger. From such reasons, in a wireless communication device using the modulation system using the multi-carrier or QAM modulation system, a high frequency amplified in a transmission part should be designed to have a high linearity and large maximum transmission power. However, a high frequency amplifier that is designed to have high linearity and large maximum transmission power generally tends to have high power consumption. As a result of the high power consumption, temperature increase in the high frequency amplifier is remarkable. Generally, in the high frequency amplifier, a plurality of power amplification elements (transistors) is connected in a parallel and multistage manner; however, because the high frequency amplifier has a temperature characteristic that a current and voltage of the transistor changes in response to the temperature, temperature compensation of the transistors is an important issue to constantly maintain a gain of the high frequency amplifier with respect to the temperature change.
For example, there is a high frequency amplification circuit that includes: a power amplification element that amplifies high frequency signals; a bias circuit that supplies a bias current to an input of the power amplification element; a constant voltage source that outputs a constant voltage; a resistance whose one end is connected to the constant voltage source; and a temperature compensation diode whose anode is connected to the other end of the resistance, whose cathode is grounded, and which performs compensation of the temperature characteristic of the diode. Even when the temperature of the diode has changed when a voltage of an anode of the temperature compensation diode is supplied to an anode side of the diode, the diode is capable of suppressing the change of a current to be supplied to the input of the power amplification element. For example, JP Laid-Open Patent Application No. 2007-306543 is known as a document related to such type of temperature compensation technology.
Also, it is difficult to design a bias power source that has a temperature characteristic that a temperature change caused by a current flowing in a transistor completely offsets a temperature change caused by a bias current. Because a difference (or gap) in the temperature compensation occurs, it is difficult to constantly maintain a gain of the power amplifier and P1dB (1dB gain compression point) with respect to the temperature change. For example, JP Laid-Open Patent Application No. 2011-176592 is known as a document of a technology that compensates a difference in the temperature characteristic by including a power source circuit that has a temperature compensation function that supplies a current or a voltage to a circuit element so as to offset a temperature change caused by a current or a voltage of the circuit element, and a temperature characteristic compensation circuit that compensates a gap between the temperature characteristic of the power source circuit and the temperature characteristic of the circuit element.
However, there is a gap in an electrical characteristic with respect to the temperature change of the power amplifier between a result of circuit simulation and a result of actual measurement of the high frequency amplifier. That is because there is a temperature distribution in the high frequency amplifier, which is an actual semiconductor, and in other words, for instance, there is a temperature difference between the inside of a high frequency amplifier part that amplifies and outputs signals input to the high frequency amplifier and the inside of the bias circuit that supplies a bias current to the high frequency amplifier part. In a conventional technology, a temperature compensation element or a temperature compensation circuit is included in the bias circuit, and a different temperature is transferred due to time-dependent temperature change in the high frequency amplifier part or amount of signals, and therefore it has been difficult to design temperature compensation with excellent accuracy.
From these reasons, there has been a problem that it is difficult to constantly maintain a gain characteristic and prevent the deterioration of a P1dB (1 dB gain compression point) characteristic because it is difficult to supply a bias current that is appropriately temperature-compensated with respect to a periphery temperature change to the high frequency amplifier part. Also, in an arrangement where the temperature compensation element is arranged in the high frequency amplification part or a temperature compensation circuit is arranged nearby, it has not been easy to suppress irregular oscillation due to the effect of a higher harmonic wave because there is a coupling of a higher harmonic wave from the high frequency amplification part.
The present application is to resolve the above-described problems, and objectives of the present invention are to propose a high frequency amplifier that can realize accurate temperature compensation in response to a temperature change of a power amplification element.